btrfs: subpage: fix the bitmap dump which can cause bitmap corruption

commit 77b0b98bb743f5d04d8f995ba1936e1143689d4a upstream.

In commit 75258f20fb70 ("btrfs: subpage: dump extra subpage bitmaps for
debug") an internal macro GET_SUBPAGE_BITMAP() is introduced to grab the
bitmap of each attribute.

But that commit is using bitmap_cut() which will do the left shift of
the larger bitmap, causing incorrect values.

Thankfully this bitmap_cut() is only called for debug usage, and so far
it's not yet causing problem.

Fix it to use bitmap_read() to only grab the desired sub-bitmap.

Fixes: 75258f20fb70 ("btrfs: subpage: dump extra subpage bitmaps for debug")
CC: stable@vger.kernel.org # 6.6+
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/fs/btrfs/subpage.c b/fs/btrfs/subpage.c
index 54736f6238e659973c95b13b670a65e883b87087..831e96b607f505bc5c3bd03137f0a35ab21be37d 100644 (file)
--- a/fs/btrfs/subpage.c
+++ b/fs/btrfs/subpage.c
@@ -766,8 +766,14 @@ void btrfs_folio_unlock_writer(struct btrfs_fs_info *fs_info,
 }
 
 #define GET_SUBPAGE_BITMAP(subpage, subpage_info, name, dst)           \
-       bitmap_cut(dst, subpage->bitmaps, 0,                            \
-                  subpage_info->name##_offset, subpage_info->bitmap_nr_bits)
+{                                                                      \
+       const int bitmap_nr_bits = subpage_info->bitmap_nr_bits;        \
+                                                                       \
+       ASSERT(bitmap_nr_bits < BITS_PER_LONG);                         \
+       *dst = bitmap_read(subpage->bitmaps,                            \
+                          subpage_info->name##_offset,                 \
+                          bitmap_nr_bits);                             \
+}
 
 void __cold btrfs_subpage_dump_bitmap(const struct btrfs_fs_info *fs_info,
                                      struct folio *folio, u64 start, u32 len)